• On the feed screen, tap the 3-line menu at the top left
• Select Settings
• Scroll down to the Community filter setting
• Type the strings you want to exclude, followed by a comma
• Exit and reopen Connect, then open a feed to see if the communities with the strings in their name are excluded

Currently, I don’t see a way to create a community on the sh.itjust.works instance. Perhaps contact one of the mods?
Or, if you have an account on another Lemmy instance that allows community creation, you could create one there.

ProtonMail app is on the IzzyOnDroid F-Droid Repo.

Direct link: https://apt.izzysoft.de/fdroid/index/apk/ch.protonmail.android

You can add the IzzyOnDroid repo to F-Droid, or Droid-ify